1. Field of the Invention
The present invention relates to a data storage apparatus and a method of data transfer and, particularly, to a data storage apparatus in which data transfer paths are connected from each controller to a cache memory, a host, a hard disk drive (HDD), and other components. The invention also relates to a method of data transfer adapted for use in this data storage apparatus.
2. Description of the Related Art
In the past, a data storage apparatus has been composed of plural modules connected to each other by dedicated data transfer paths, each module being made of a drive interface, a controller for controlling transfer of data, data transfer paths interconnecting the interface and controller, and a microprocessor for controlling the whole system, a host interface, a cache memory, and other components. Electric power is supplied to the modules from power supplies independently. Each module writes data transferred from a host into cache memories of the modules. Because of this countermeasure, loss of transferred data is avoided, and the reliability of the system is enhanced (patent reference 1).
To transfer data along dedicated data transfer paths interconnecting the modules, data transferred to the cache memories of other modules, data transferred among the host interface, drive interface, and cache memories, and control data shared between processors are time shared, multiplexed, and transferred. In some cases, transferred data may be different greatly in transfer length according to transfer sources and transfer destinations. For example, when a microprocessor transfers control data to a host interface or a drive interface, control data sets shorter in transfer length than other data sets are frequently transferred. Control data sets having short transfer lengths are time shared and multiplexed on dedicated data transfer paths with data sets having large transfer lengths. Overhead produced when data is multiplexed delays data transfer between source and receiver. There is a tendency that the transfer time is increased. Furthermore, there is the tendency that data transfer times vary more widely for the same reason.
One example of method of suppressing the transfer time and differences in the transfer time is disclosed in patent reference 2. In particular, data transferred in various transfer channels are converted into cells (packets) in the common format. Cells to be transferred to the same destination are time shared and multiplexed. The method permits differences in delay time between transfers of data along the various transfer channels to be suppressed.    [Patent reference 1] JP-A-2005-44010    [Patent reference 2] JP-A-2001-119412